Felipe Galván-Magaña

Diet composition of sailfish (Istiophorus platypterus) from the southern Gulf of California, Mexico

Diet composition of the sailfish Istiophorus platypterus from the southern Gulf of California was determined using stomach contents of 576 fish. They were sampled from 1989 to 1991 from the sport fishing fleet at six tourist ports of the Mexican Pacific (La Paz, Cabo San Lucas, Mazatlan, Puerto Vallarta, Barra de Navidad, and Manzanillo). A total of 78 different prey taxa was classified and 64 were identified to species. From the diet composition and using the percent of index of relative importance (IRI), three feeding zones were determined by using cluster analysis. The most important prey by zones were in Zone I, La Paz: Dosidicus gigas, Scomber japonicus, and Auxis spp.; Zone II, Cabo San Lucas: Auxis spp., Selar crumenophthalmus, and Lagocephalus lagocephalus; and Zone III, Mazatlan, Puerto Vallarta, Barra de Navidad, and Manzanillo: Argonauta spp., D. gigas, and Auxis spp. We suggest that sailfish in Mexican Pacific waters are generalist predators feeding mainly on epipelagic species in coastal and oceanic waters, and occasionally diving to prey on demersal fish. The changes in diet composition among zones seem to be related more to abundance and distribution of the prey than to food preferences.

Diet of blue marlin Makaira mazara off the coast of Cabo San Lucas, Baja California Sur, Mexico

Abstract Analysis of the stomach contents of 204 blue marlin ( Makaira mazara ) caught by the sport-fishing fleet of Cabo San Lucas in the southern Gulf of California is presented. The specimens sampled were caught during the summer and fall of 1987, 1988, and 1989 when the sea is warm (28–30°C). Blue marlin were found to feed on 35 prey species, 3 of which represented 90% of the total stomach contents by frequency of occurrence. The main prey were epipelagic organisms from the oceanic zone and demersal fishes from the neritic zone. The most important prey were bullet mackerel Auxis spp., young finescale triggerfish Balistes polylepis , and the giant squid Dosidicus gigas .

Embryonic bicephaly in the blue shark, Prionace glauca , from the Mexican Pacific Ocean

A case of bicephaly in embryos of the blue shark Prionace glauca in the Mexican Pacific Ocean is described. Malformed female shark embryos were found in pregnant females caught in the Gulf of California (Punta Arenas) and off the western coast of Baja California Sur, Mexico (San Lazaro). Abnormal sharks showed a symmetric bicephaly that could be caused by the high number of embryos found in the uterus of the blue shark, which is the most fecund species of shark in the world. The abnormality probably began during the embryonic development.

Oxidative stress indicators and trace elements in the blue shark (Prionace glauca) off the east coast of the Mexican Pacific Ocean.

Trace element concentrations and oxidative stress indicators (including production of reactive oxygen species (ROS), antioxidant enzyme activities and oxidative damage) were measured in muscle of blue sharks collected along the west coast of Baja California Sur to determine potential differences by sex and maturity cohorts. Mercury (Hg) concentration in muscle samples from larger sharks (>200 cm LT) exceeded the permissible limit (>1 ppm wet weight) for human consumption set by numerous international agencies. Significant differences were found in Hg concentrations (mature>immature; males>females), and in protein carbonyl concentrations (male>female); however, except for carbonyl protein levels, no significant differences by sex or maturity stage were found in the oxidative stress indicators. Differences between sexes and maturity stages in trace element concentration and carbonyl protein levels in blue shark muscle may be related to variations in diet within different cohorts.

Superoxide production, oxidative damage and enzymatic antioxidant defenses in shark skeletal muscle.

Pelagic sharks, unlike teleost fish, require constant active swimming to obtain a suitable oxygen (O(2)) supply. An increase in O(2) consumption during exercise enhances production of reactive oxygen species (ROS). We hypothesized that shark species that display vigorous exercise, such as Isurus oxyrinchus and Carcharhinus falciformis, have higher ROS production and, in consequence, higher antioxidant enzyme activities in muscle in comparison with species with less active swimming, like Sphyrna zygaena. Superoxide radical (O(2)(*-)) production, lipid peroxidation levels (TBARS) and the activity of antioxidant enzymes: superoxide dismutase (total, t-SOD; manganese-dependent, Mn-SOD, and copper and zinc-dependent, Cu, Zn-SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR), were measured by spectrophotometric assays in skeletal muscle extracts of three shark species (C. falciformis, I. oxyrinchus and S. zygaena). Higher O(2)(*-) production and GPx and GST activities (p<0.05) were found in C. falciformis and I. oxyrinchus than in S. zygaena. These results suggest that in antioxidant enzymes (GPx, GST) activity suffices to balance the production of ROS and to maintain lower TBARS levels (p<0.05) than in C. falciformis or S. zygaena, contributing to the capacity of I. oxyrinchus to maintain high muscular activity.

Diet and trophic position of the devil rays Mobula thurstoni and Mobula japanica as inferred from stable isotope analysis

This study confirms the diet and determines the trophic position of the bentfin devil ray ( Mobula thurstoni ) and spinetail devil ray ( Mobula japanica ) in the south-west Gulf of California. There has been an active fishery in the area for these filter-feeding elasmobranchs, which are highly susceptible to exploitation due to low fecundity and long lifespan. However, information on their basic biology is scarce. δ 13 C and δ 15 N values of devil rays and zooplankton (sorted according to trophic level: herbivores, carnivores and omnivores) were determined over a period of 11 months, to allow for isotopic temporal variations in isotopic signals at the base of the food web. On the basis of fractionation factors we determined that bentfin and spinetail devil rays fed mainly on Nyctiphanes simplex , the most abundant euphausiid in neritic waters of the Gulf of California. The trophic positions obtained for the devil rays correspond to second level consumers.

Trophic dynamics and seasonal energetics of striped marlin Tetrapturus audax in the southern Gulf of California, Mexico

The analysis of consumption and energy storage of the striped marlin (Tetrapturus audax) during a yearly cycle in the southern Gulf of California, Mexico using calorimetric methodology is presented. The great diversity of prey species in striped marlin stomachs confirms their generalist feeding pattern with a high predatory capacity, foraging mainly on epipelagic organisms from neritic and oceanic zones. According to the index of relative importance (IRI), the most important prey were the chub mackerel Scomber japonicus (28%), California pilchard Sardinops caeruleus (27%), and jumbo squid Dosidicus gigas (7.7%), contributing up to 80% of the energy for striped marlin in this area. Analysis of the energetic dynamics suggested that major energy intake and storage of energy in the muscle, and ovary occur during the summer (August 1994). The southern Gulf of California is a migration zone of the striped marlin, in which the smaller marlin are consuming and storing energy to be prepared for reproduction, which may occur in an area, reported but unverified, south of the southern tip of Baja California (Revillagigedo Islands).

Biomagnification of mercury and its antagonistic interaction with selenium in yellowfin tuna Thunnus albacares in the trophic web of Baja California Sur, Mexico

Mercury and selenium concentrations were determined in muscle of 37 yellowfin tuna (Thunnus albacares) captured aboard of Mexican purse-seiners boats off western coast of Baja California Sur, between Punta Eugenia and Cabo Falso, from October to December 2006. Also, its prey (mainly, jumbo squid Dosidicus gigas and pelagic red crab Pleuroncodes planipes) were analyzed from the stomach contents. All the mercury values obtained were lower that mercury content recommended by standard legal limits for seafood adopted by Mexican norms (typically 0.5-1.0μg g(-1)). Mercury concentrations vary between 0.06 and 0.51μg g(-1) in yellowfin tuna, and from 0.01 to 0.20μg g(-1) in its prey, suggesting that mercury can accumulate in prey tissues and that of their predator. Biomagnification factors (BMF) between predator-prey associations were calculated. The BMFs were >1, indicating that mercury biomagnifies along the food web of yellowfin tuna. In all species studied there was a molar excess of selenium over mercury. The rank order of mean selenium/mercury molar ratios was for pufferfish (42.62)> diamond squid (15.09)>yellowfin tuna (10.29)>pelagic red crab (10.05)>panama lightfish (9.54)> jumbo squid (8.91). The selenium health benefit value (Se-HBV) was calculated to have an improved understanding of the health benefits and risk of fish consumption.

Age and growth of the blue shark, Prionace glauca Linnaeus, 1758, in the Northwest coast off Mexico

El tiburon azul es una de las principales especies capturadas en la pesqueria artesanal en la costa noroeste de Mexico. En ella, se estimo la edad y el crecimiento mediante el conteo de las bandas de crecimiento en el centro de las vertebras de 204 tiburones utilizando nitrato de plata para tenir los centros. Los tiburones se encontraron en un rango de tallas entre 81 y 270 cm de longitud total (LT), con un promedio de 165 �} 35 cm y una proporcion sexual de machos y hembras de 2:1. Los machos presentaron LT entre 81 y 270 cm (150,3 �} 32,3 cm, n=593) mientras que las hembras se encontraron entre 90 y 252 cm TL (162,7 �} 37,5 cm, n=324). La relacion entre la LT y el radio del centro (CR) fue lineal indicando una relacion positiva entre el crecimiento del centro de las vertebras y el crecimiento del organismo. El valor estimado del IAPE fue de 3,0%. La edad maxima estimada en los machos fue 16 anos y en las hembras, 12 anos. La mayoria de los tiburones en las capturas fueron juveniles de edad cuatro (134 �}13 cm TL) y siete (174 �} 21 cm TL) de los cuales 19% fueron machos y 22% hembras. Los parametros de crecimiento de von Bertalanffy fueron: L�� = 299,85 cm TL, K = 0,10 anos-1, y t0 = .2,44 anos para machos y L�� =237,5 cm TL, K = 0,15 anos-1, y t0 = .2,15 anos para hembras, encontrandose diferencias en el crecimiento entre sexos. Los parametros de crecimiento estuvieron dentro del rango de valores previamente reportados para tiburon azul en el Oceano Pacifico.

Trophic shift in the diet of the pelagic thresher shark based on stomach contents and stable isotope analyses

Abstract The trophic ecology of the pelagic thresher shark (Alopias pelagicus) was analysed using stomach contents and carbon (δ13C) and nitrogen (δ15N) stable isotope analysis. The sharks were caught in Ecuadorian waters between June and December 2003. Approximately 24 prey species were found in the stomachs of 111 sharks. The most common species were Dosidicus gigas, Benthosema panamense and Sthenoteuthis oualaniensis. Mean (± SD) muscle isotope values of the pelagic thresher shark were −16.0±0.3‰ for δ13C and 13.7±1.1‰ for δ15N; mean (± SD) vertebrae values were −16.7±2.0 for δ13C and 9.4±1.8 for δ15N. There were no significant sex-related differences in muscle δ13C and δ15N; however, female vertebrae had significantly higher mean (± SD) δ13C values (−16.4±2.0‰) than males (−18.8±0.3‰). Inter-individual variation in δ15N values was observed in both tissues and was likely related to foraging in different ecosystems with distinct isotope values. Both stomach content and isotope data suggest that the pelagic thresher shark is a specialist predator in Ecuadorian waters. In general, little is known about the foraging ecology and movement patterns of this globally distributed but elusive top marine predator, and how these fundamental ecological traits vary among populations. By using two independent but complementary approaches, our study addresses these questions for the pelagic thresher sharks in Ecuadorian waters. Such information is critically important for the design of effective management strategies for these highly exploited but poorly understood predators.